The Mercedes-AMG GT will receive a mild power upgrade and subtle cosmetic tweaks later this year as part of its mid-life facelift.

Due on sale in Britain in December, the updated Porsche 911 rival has been spotted testing with light camouflage on its bumpers to hide changes made there. The most recent sighting is of a convertible (below).

The changes are set to be minor because AMG only last tweaked the exterior design of its sports car after the launch of its GT R and GT C models in late 2016. The changes included fitment of a larger Panamerica front grille.

The GT, which was introduced to Mercedes' line-up in 2014, will also get a small upgrade in power from its turbocharged eight-cylinder engine.

The current standard car produces 469bhp from its 4.0-litre V8, but the unit produces up to 577bhp in the Mercedes-AMG GT R, showing how much available room for performance there is. Expect the base model to edge towards 500bhp, with the S and C models above it also raising their current 515bhp and 549bhp respective outputs.

The top AMG GT R could also receive a boost, although that car's output is understood to be limited by the fitment of a dry sump. AMG may choose to integrate the wet sump system of the E63, which produces 603bhp in the S that uses the same V8, to enable a more substantial increase.

The updated AMG GT range will come at the tail end of a heavy range expansion for AMG, where a new GT four-door model will be launched. Although linked in name, the car will be more technically related to AMG E-Class models than the GT sports car.

AMG is also launching a new hybrid line-up, which starts with the CLS 53 later this year, to kick-start a performance electrified range. However, there are no plans to integrate hybrid technology into the current GT model.